From left to right they are
1 'nt' in a square/rectangle
2 '925' in an oval
3 what looks like a circle with a cross through it in an oval
4 what looks like an o or a u with an open top, in a square. I wonder whether it might be a Hebrew letter?
Sorry the photos are so bad - they are absolutely tiny and I don't have a very good camera. (Each shell is 14 mm across).
Any help in identifying these would be really gratefully received. Thank you.

